For DMT to work orally, the addition of something referred to as a monoamine oxidase inhibitor (MAOI) is required.  MAOIs such as harmine inhibit the production of the stomach enzyme and this allows orally ingested DMT to become effective.

Naturally occurring MAOIs in combination with naturally occurring DMT have a tradition of use in native South American cultures.  Here the resultant brew is most famously referred to as ayahuasca (other names include yage and caapi)

The classic plant sources for MAOIs and DMT in ayahuasca include the Amazonian vine Banisteriopsis caapi (which contains the MAOI harmine) and Psychotria viridis (containing DMT). 

Other plants can be used, for example, Syrian rue (Peganum harmala), as a source of harmine. 

Syrian Rue has no history of traditional usage; in fact the plant is not originally native to South America. 

In such cases, where at least one of the principle admixtures is a variant like this, the brew is more properly referred to as an ayahuasca analogue.

Among Ayahuasquera ~ Terence McKenna's account of an Amazonian adventure